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Supplemental Digital Content is available in the text.

Singlet molecular oxygen (1O2) has well-established roles in photosynthetic plants, bacteria and fungi1–3, but not in mammals. Chemically generated 1O2oxidizes the amino acid tryptophan to precursors of a key metabolite called N-formylkynurenine4, whereas enzymatic oxidation of tryptophan to N-formylkynurenine is catalysed by a family of dioxygenases, including indoleamine 2,3-dioxygenase 15. Under inflammatory conditions, this haem-containing enzyme is expressed in arterial endothelial cells, where it contributes to the regulation of blood pressure6. However, whether indoleamine 2,3-dioxygenase 1 forms 1O2and whether this contributes to blood pressure control have remained unknown. Here we show that arterial indoleamine 2,3-dioxygenase 1 regulates blood pressure via formation of 1O2. We observed that in the presence of hydrogen peroxide, the enzyme generates 1O2and that this is associated with the stereoselective oxidation of l-tryptophan to a tricyclic hydroperoxide via a previously unrecognized oxidative activation of the dioxygenase activity. The tryptophan-derived hydroperoxide acts in vivo as a signalling molecule, inducing arterial relaxation and decreasing blood pressure; this activity is dependent on Cys42 of protein kinase G1α. Our findings demonstrate a pathophysiological role for 1O2in mammals through formation of an amino acid-derived hydroperoxide that regulates vascular tone and blood pressure under inflammatory conditions.

The chromophore, BODIPY 581591, has an extended conjugated system that reacts with oxygen centeredradicals leading to changes in its spectral characteristics. Fatty acidconjugated BODIPY 581591 transfers readily between membrane bilayers and can be used as a sensor of oxidative stress in cell populations. We report here the use of a phosphatidylcholine PC derivative of BODIPY 581591, which transfers much less rapidly between membranes. This allows the analysis of oxidative stress in individual cells and in different compartments within cells. Quantitative imaging and flow cytometry were used to measure the ratio of fully conjugated to oxidized probe in model systems and in Plasmodium falciparuminfected erythrocytes. We observed an increase in the oxidation of the parasiteassociated BODIPY 581591PC as the intraerythrocytic parasite matures. By contrast, BODIPY 581591PC associated with the erythrocyte membrane experiences a low level of oxidation even in the later stages of parasite development. Treatment with a prooxidant compound caused increased oxidation of the probe in the parasite compartment, but less so in the host cell membrane. Conversely, treatment with ferricyanide increases oxidation of the probe in the erythrocyte cell membrane but does not inhibit parasite growth. Chromatographic analysis of the lipids in infected erythrocytes shows no evidence for loss of αtocopherol or the accumulation of lipid hydroperoxides indicating that, despite the increased oxidative stress, the parasite membranes remain protected from substantial lipid oxidation. We have established BODIPY 581591PC as a useful probe of the spatial distribution of oxidative stress in P. falciparuminfected erythrocytes; however, the probe appears to be more sensitive to oxidative damage than endogenous lipids. © 2009 International Society for Advancement of Cytometry

Catalytic DNA molecules that target the transcription factor c-juninhibit skin cancer growth in mice.